Morphospace of foraminiferal shells: results from the moving reference model

The moving reference model of foraminiferal tests (shells) is based on principal morphogenetic rules revealed from real foraminifera. The model has introduced apertures as moving reference points based on minimization of the distance between them. These modifications greatly enhanced variability of simulated shells closely resembling actual complexity of small polythalamous foraminifers. The resulted theoretical morphospace of all simulated forms is far more extensive than any produced before. The fragments of the multidimensional theoretical morphospace are presented in two forms, i.e. a (classical) box model and a morphotree. The theoretical morphospace of foraminifera reveals regions of the morphospace that include similar forms. These specific fields in the morphospace, called morphophases, are separated from each other by either sharp or gradual morphophase transitions, which involve sharp or gradual changes in morphology controlled by changes of the model parameters. Optimized emplacement of foraminiferal apertures is responsible for these morphophase transitions. The overall morphospace splits into the 'possible range' and the 'forbidden range'. The 'possible range' includes existent and nonexistent foraminiferal forms, which are further separated into 'vacant', 'dysfunctional', and 'deficient' ranges. All the ranges provide additional knowledge on theoretical foraminiferal morphology. The 'vacant range' of possible, although nonexistent, morphologies is limited and that may suggest that the real evolution of foraminifera has discovered most of the morphologic possibilities. It is suggested that the 'forbidden' and 'deficient' ranges present model constraints useful for understanding morphogenesis, which may be tested by further modifications of the model. The analysed theoretical morphospace verifies the moving reference model, indicating the fundamental role of apertures in the morphogenesis of foraminifera.     

First beetle elytra,abdomen (Coleoptera) and a mine trace from Lunz (Carnian,Late Triassic,Lunz‐am‐See,Austria) and their taphonomical and evolutionary aspects

Abstract: Four new species of Permosynidae are described: Platycrossus caroli Ponomarenko in Meller et al. sp. nov., Hydrobiites handlirschi Ponomarenko in Meller et al. sp. nov., Ademosyne polyzetete Ponomarenko in Meller et al. sp. nov. and Diarcuipenna bennettitophila Ponomarenko in Meller et al. sp. nov. Together with one polyphagous abdomen, they represent the first beetle remains from the Lunz formation, known for its richness in bennettite and cycad leaf remains and also for the bennettite reproductive organs. Furthermore, the first insect mine trace on a Nilssonia leaf segment is described, which is one of the most ancient linear mine traces. The rareness of insect remains in the plant‐bearing layers of the Lunz formation is still an enigma from the taphonomical–chemical point of view. The palaeoentomological and palaeobotanical considerations tentatively indicate a relationship between the rare occurrence of coniferous plants and the evolution or radiation of phytophagous insects during this time.     

Trading safety for food: evidence from gut contents in roach and bleak captured at different distances offshore from their daytime littoral refuge

1. Regular diel habitat shifts in roach were detected by hydro‐acoustics in five moderately eutrophic, stratifying (maximum depth 24–27 m) and approximately circular lakes (of surface area 15, 75, 125, 300 and 900 ha and diameters 250, 600, 1000, 1700 and 2600 m) in north‐eastern Poland in the years 1998–2000, when the lakes were free of smelt and other typical offshore planktivores, and their offshore areas were completely free of fish during the day. 2. The diel change in roach distribution was shown to assume a similar pattern in each lake: fish migrated from a daytime littoral refuge towards the centre of the lake at dusk, and returned to the littoral refuge at dawn. After sunset, fish gradually dispersed offshore until they covered the entire lake area in each of the three smaller lakes. In each of the two larger lakes, only small numbers of fish were seen in the central area at night, implying that the centre of the lake retained high food availability throughout the summer. 3. Inshore–offshore gradients in zooplankton prey density, body size, and numbers of eggs per clutch were weak or undetectable in the two smallest lakes, but strong and persistent in the three larger lakes, with Daphnia densities 5–30 times as high and body length 1.2–1.5 times as great in the central area as inshore. 4. The likely increase in the potential predation risk with distance from the littoral daytime refuge was found to be compensated by increased food gains in those fish which moved offshore at dusk to feed within a short time window, when light intensity was lower to make the risk reduced, but still high enough to see zooplankton prey. The benefit because of increased prey acquisition was greatest in the centre of the largest lake (at 1300 m from the shore), as revealed from gut inspections of roach and bleak trawl‐sampled at different distances from the edge of the reed belt, and seen as a gradual, order‐of‐magnitude increase in the volume of food in the foregut, The food volume against distance‐from‐shore regression was highly significant on each of the four sampling dates in the largest lake, in spite of the wide variability of food volume in individual fish.     

LIGHT, GRAVITY AND CONSPECIFICS AS CUES TO SITE SELECTION AND ATTACHMENT BEHAVIOUR OF JUVENILE AND ADULT DREISSENA POLYMORPHA PALLAS, 1771

Dreissena polymorpha, the zebra mussel, is one of the mostimportant components of the aquatic ecosystems it inhabits,due to high densities and filtration rates of this fouling organism.This laboratory study deals with several physical and biologicalfactors influencing zebra mussel juveniles (<10 mm) and adults(>10 mm) site selection behaviour and their byssal attachmentto substrate. Mussels preferred black substrate rather thanwhite. This preference was found to be stronger in smaller individuals.Furthermore, all mussels, independently of their size, selectedshadowed sites and avoided illuminated ones. Large mussels attachedmore often in darkness than in light, while for small specimenslight conditions made no difference. Large mussels tended toattach to lower parts of vertical test-tubes, while the numbersof small specimens in both halves of the test-tubes were similar.If initial conditions, used by mussels to select their attachmentsite, were changed by turning the test-tubes upside down, smallindividuals detached and looked for a new site more frequentlythan large ones. Large mussels attached more often in higherdensities of conspecifics, but physical contacts among conspecificsand their size composition seemed to have no impact on attachment.This study shows that many environmental stimuli influence locomotionand attachment of post-metamorphic zebra mussels. Therefore,the behaviour of this group may impact upon adult distributionobserved in field. Preferences exhibited by mussels lead tothe creation of dense aggregations in dark, deep places, providing protectionagainst dessication, predators and excessive water flow. (Received 18 April 2000; accepted 5 October 2000)